In the field of power assistance for vehicle steering systems, for example in the field of power-assisted steering systems, it is known to provide an electric motor by means of which the torque for providing power assistance is applied to the corresponding vehicle steering system, or the corresponding steering gear. A power assistance system is usually composed here of a control circuit (ECU) and an electric motor which is controlled by this ECU. The power assistance system can make available here an assistance force, that is to say an assistance torque, which is intended to reduce the activation forces applied by a driver via a steering wheel. A power assistance system can, however, also make available an additional steering angle, for example in the case of a superimposition steering system in which the steering angle applied by the driver is changed by an additional transmission means. By means of such a power assistance system, it is, for example, also possible to input additional steering movements, for example in the case of automatic lane keeping of the vehicle or for automatic parking.
The electric motor is usually controlled here by means of a control circuit, wherein the control circuit comprises a motor controller and power switches for controlling the power flows for the electric motor are provided. For example MOSFETs may be provided by means of which the power current which is fed to the electric motor is controlled.
The known control circuits which, in addition to the one or more power switches, also comprise control electronics, are usually connected to the electric motors which apply the torque and are protected against environmental influences by means of a housing.
In the case of electric power assistance systems it is desired to form a compact assembly of the electric motor, electronic control circuit and possibly a transmission by means of which the torque produced by the electric motor is applied to the steering system. In this context, good dissipation of heat from the power switching elements which control the energization of the electric motor is to be preferably ensured. Furthermore, a good seal must be provided against environmental influences, such as dust, dirt and moisture, over the entire service life of the power assistance system.
Such an arrangement is known, for example, from DE 10 2007 048 075 A1, in which the control circuit is protected against environmental influences by means of a housing cover which is connected by flanges to the electric motor.
DE 10 2009 029 538 A1 discloses a steering device, in particular an electric power steering device for a motor vehicle, in which an electric control unit is attached to the housing of the electric motor by means of flanges.
Since the electronics and the power components are very sensitive to dust, swarf or other soiling, the corresponding electronics components must be mounted on the electric motor in a clean room, and any ingress of dust, dirt and swarf into the housing of the electronic control circuit has to be prevented. Dirt, dust or swarf can specifically lead to short circuits which would ultimately constitute a safety risk as a result of the power steering assistance.